This invention relates to a paper size composition and to a method for sizing paper and paperboard therewith. More particularly, the invention relates to a paper size composition comprising a mixture of an internal size and a long chain alkyl derivative of starch or gum.
Paper and paperboard are often internally sized with various hydrophobic materials including, for example, alkyl ketene dimers, anhydrides of fatty acids, maleated triglycerides, maleated alpha-olefins, maleated fatty acids as well as substituted linear or cyclic dicarboxylic acid anhydrides. These sizes are introduced during the actual paper making operation and, as such, require that the sizing compounds be uniformly dispersed throughout the fiber slurry in a small particle size.
It has been general practice to add the sizes in the form of an aqueous emulsion prepared with the aid of emulsifying agents including, for example, cationic or ordinary starches, carboxymethyl cellulose, natural gums, gelatin, cationic polymers or polyvinyl alcohol, all of which act as protective colloids. The use of such emulsifying agents with or without added surfactants did, however, suffer from several inherent deficiencies in commercial practice. A primary deficiency concerned the necessity of utilizing relatively complex, expensive and heavy equipment capable of exerting high homogenizing shear and/or pressures, together with rigid procedures regarding emulsifying proportions and temperatures, etc., for producing a satisfactory stable emulsion of the particular size. Additionally, the use of many surfactants in conjunction with protective colloids was found to create operational problems in the paper making process such as severe foaming of the stock and/or loss in sizing.
With particular reference to the procedures of the prior art which utilized these internal sizing agents, it was necessary in commercial practice to pre-emulsify with cationic starch and/or other hydrocolloids using relatively rigid procedures with elevated temperatures to cook the starch or hydrocolloids and high shearing and/or high pressure homogenizing equipment. Unless these complicated procedures were carefully followed difficulties such as deposition in the paper system, quality control problems and generally unsatisfactory performance were often encountered.
Many of these problems were overcome by the teachings of U.S. Pat. No. 4,214,948 and U.S. Pat. No. Re. 29,960 which disclosed the use of a size mixture of specific sizing agents and polyoxyalkylene alkyl or alkyl-aryl ethers or their corresponding mono- or di-esters, which mixtures were easily emulsifiable with water in the absence of high shearing forces and under normal pressure. Despite the contributions of the latter patents there remains a need in the art for emulsions exhibiting improved sizing performance and operability.